An electronic camera for capturing an image by using an image sensing element such as a CCD (Charge-Coupled Device) for converting light incoming through a photographing lens has an electronic shutter function of controlling the image sensing time by controlling the imaging sensing operation time for receiving light which forms an image. Usually, the electronic camera also has a mechanical shutter for reducing smear or the like caused by redundant light after the image sensing element has received a necessary quantity of light. Further, the electronic camera performs slit exposure using a focal plane shutter, like exposure of a general silver halide film.
As this electronic camera, an electronic camera disclosed in Japanese Patent Laid-Open No. 11-212136 (to be referred to as the first prior art hereinafter) uses a mechanical shutter to control exposure in normal natural light photography, and uses an electronic shutter to control exposure in high-speed photography using an electronic flash device.
As the above-mentioned electronic camera, the following electronic camera is disclosed in Japanese Patent Laid-Open No. 11-234574 (to be referred to as the second prior art hereinafter). When exposure is controlled by mechanical and electronic shutters, the driving start timing of the mechanical shutter or the charge accumulation start timing of the electronic shutter is adjusted to adjust an individual variation error caused by a mechanical delay until actual operation of the mechanical shutter starts in response to an electrical driving start signal for designating a shutter operation in the mechanical shutter since the electrical driving start signal is issued.
In the first prior art, however, the mechanical shutter controls exposure in normal natural light photography, and the highest speed of a shutter speed generally adopted in the electronic camera depends on the performance of the mechanical shutter. Achievement of a high speed of, e.g., 1/8,000 sec requires a high-performance mechanical shutter. The shutter itself becomes a complicated mechanism, resulting in a large shutter and high cost. The mechanical shutter is technically difficult to drive at a high speed (e.g., 1/16,000 sec or more).
In the first prior art, the mechanical shutter is generally driven by starting driving of a front blade in response to a front blade driving start signal after the end of a photographing sequence for a preceding frame. The end of driving the front blade is detected by a switch for detecting the end of driving the front blade. Charges are accumulated by a CCD or the like. After charge accumulation ends, driving of a rear blade starts in response to a rear blade driving start signal. The end of driving the rear blade is detected by a switch for detecting the end of driving the rear blade. Then, normal read of signal charges is performed. This arrangement warrants reliable exposure control. However, since the next operation starts upon the end of each operation, the time taken for a photographing sequence per frame is prolonged. Since the next operation starts after the operation status of each switch is monitored, the time taken for a photographing sequence is prolonged. This disables high-speed sequential shooting of an electronic camera.
In the second prior art, variations in exposure control time caused by the mechanical delay between the mechanical shutters of respective electronic cameras are corrected by adjusting the application timing of a mechanical shutter driving pulse or the charge accumulation start timing of the electronic shutter. This adjustment is done for each electronic camera, which increases the time taken to assemble and adjust the electronic camera, and increases the cost. This electronic camera requires a jig for measuring and adjusting variations in exposure time caused by the mechanical delay of the mechanical shutter. If the charge accumulation start timing of the electronic shutter is adjusted, the release time lag of the electronic camera varies between respective electronic cameras. This is inconvenient for a user who uses a plurality of electronic cameras because photographs taken by releasing the shutters of the electronic cameras become different.